1. Technical Field
The present invention relates to an intermediate transfer belt equipped in image forming apparatuses such as copiers and printers and a method of preparing the same, and to an image forming apparatus.
2. Description of the Related Art
In the conventional art, a belt, especially a seamless belt, has been used for various purpose, as a member in an electrophotographic image forming apparatus. In recent years, an intermediate transfer belt system has been used in a full color image forming apparatus, where the intermediate transfer belt system includes superimposing developed images of four colors, yellow, magenta, cyan, and black temporarily on an intermediate transfer member, and collectively transferring the superimposed images onto a transfer medium, such as paper.
As for the aforementioned intermediate transfer belt, a system using developing units of four respective colors to one photoreceptor has been used, but this system has a problem that a printing speed thereof is slow. Accordingly, to achieve high speed printing, a quarto-tandem system has been used, where the tandem system includes providing photoreceptors of four respective colors, and an image of each color is continuously transferred to paper.
In this system, however, it is very difficult to accurately position images of colors to be superimposed, as the paper is affected by the fluctuations of the environment, which causing displacement of the colors in the image. Accordingly, currently, an intermediate transfer belt system has been mainly adapted for the quarto-tandem system.
Under the circumstances as mentioned above, the higher requirements for properties (high speed transferring, and accuracy for positioning) of a intermediate transfer belt have been demanded than before, and therefore it is necessary for an intermediate transfer belt to satisfy these requirements. Especially for the accuracy for positioning, it has been required to inhibit variations caused by deformation of an intermediate transfer belt itself, such as stretching, after continuous use thereof. Moreover, an intermediate transfer belt is desired to have flame resistance as it is provided over a wide region of a device, and high voltage is applied thereto for transferring. To satisfy these demands, a polyimide resin that is a highly elastic and highly heat resistant resin, has been mainly used as a material of an intermediate transfer belt.
When the intermediate transfer belt is used in an image forming apparatus for long periods, the edge of the belt cracks or the belt breaks when curved by a drive roller. Therefore, the running belt does not have sufficient durability.
Japanese Patent No. JP-4840038-B2 (Japanese published unexamined application No. 2007-14754-A) discloses a method of specifying a volatile material in an intermediate transfer belt to be 10 to 100,000 ppm to improve durability and transferability thereof. This relates to improvement of durability of a surface layer, and is different from the present invention in technological thought.
Japanese Patent No. JP-4356508-B2 (Japanese published unexamined application No. 2005-163007-A) discloses an intermediate transfer belt using a polyamic acid prepared with a mixed solvent including γ-butyrolactone and N-methyl-2-pyrrolidone. However, N-methyl-2-pyrrolidone is likely to remain as a residual solvent and resistivity is likely to change at low (high) temperature and low (high) humidity, resulting in image density of the resultant images is likely to change. N-methyl-2-pyrrolidone has high hygroscopicity and the belt is likely to change in sizes.
The polyimide is typically a very expensive material, and polyamideimide is widely used instead. The polyamideimide has higher hygroscopicity than the polyimide, and is not only poor in size stability but also low in flexibility as a resin. Therefore, the polyamideimide is low in durability. i.e., likely to crack and cut.
Because of these reasons, a need exists for an intermediate transfer belt having high durability, producing high quality images without change of image density even when the environment drastically changes.